In the end of the Garg Sanhita, Gargacharya Ji does indeed make some predictions about kaliyug. Gargacharya was the acharya of the Yadu vansh during the time of Shree Krishna's avatar. In other words, he was the kul Guru of both Nand Baba and Vasudev during that time (about 5,000 years ago). This precedes the existence of all the current sampradays. Nonetheless, he predicted the coming of four great Saints: Vishnu Swami, Madhvacharya, Ramanujacharya and Nimbarkacharya. He said that each, respectively, would be ansh of Vaman, Brahma, Balram (Shesh Nag) and Sanat Kumar. He said that they would be the founders of sampradays in kaliyug. He did not say that these would be the only true Saints or the only sampradays.He then states literally that, "People should follow in the path of a sampraday, because a mantra which is 'sampraday viheen' (without sampraday) is 'nishphal' (fruitless). Again, he did not say explicitly that you had to follow one of those four sampraday only. In our Hindu tradition, we understand the importance of a true Saint's guidance on the path to God. However, there have been thousands of vaishnav Saints to grace the earth in the last few hundred years. Many of their brief life histories are available in the 'Bhakt Maal' which has been recognized as an authentic account. Not all of those Saints belonged to one of those 4 sampradays.The Mundak Upnishad defines who is qualified to be a Guru: he must be 'shrotriya' and 'brahmanishth', or learned in all the scriptures, and God realized. In other words, once a soul is God realized, they are qualified to guide people on the path to God. From this point of view, you could say that every God realized Saint has their own sampraday, because they are all teaching the true path to God. Thus, the practice of devotion done with the guidance of a true Saint will be fruitful, and the practice of devotion done without the guidance of a true Saint will be 'nishphal'.At this point I would like to share the wisdom given to us by Jagadguru Shree Kripalu Ji Maharaj regarding sampradays. He says that truly there are only 2 sampradays, and both have existed since eternity. There is the mayic sampraday and the Godly sampraday. Why? Because there are 3 eternal existences: God, the souls and maya. Thus, the souls have only 2 directions in which they can progress: either towards God, or towards maya. Those teachings, traditions and Saints who encourage us towards God are part of the Godly sampraday, and those who encourage us towards maya are part of the mayic sampraday. Thus, all true Saints are part of the same sampraday and only try to guide the souls towards God. Any further identification with a particular sampraday on a more minute level only serves to keep us apart and give us reason to disagree. What we need in today's world is to promote unity.In general, I would say that Hinduism tends to be inclusive, not exclusive. What I mean is that regarding the path to God, Hinduism teaches spiritual principles that can be applied universally by all people. The application of these principles is not reserved for only certain people who belong to a certain sampraday. For instance, the Vedas say 'bhaktirevainam nayati bhaktirevainam pashyati bhaktirevainam darshayati bhakti vashah purusho bhaktirev bhooyasee', which means that God is only attainable through bhakti. This statement may appear at first glance to be exclusive ("If you don't follow the path of bhakti, you can never reach God"). However, if you understand that bhakti means attaching the mind to God with 100% faith, then the statement becomes inclusive, because anyone of any ethnic or religious background who attaches their mind to God with 100% surrender, can attain God. So we see that the general spiritual principle is that God is attainable by surrendering our mind to Him to receive His Grace. And this principle can be understood and adopted by anyone, regardless of what religion or sampraday they belong to.Once someone accepts this general principle, then arises the question of how to implement it in a daily practice (or sadhana bhakti). The practice of 'Navdha Bhakti' (nine ways of devotion) is most famous in the Vaishvav tradition, as described by Bhakt Prahlad in the Bhagwatam. However, even the Bhagwatam, at various places, describes more than 30 ways of practicing devotion. Why is this so? Because true bhakti means that your mind is in God. All other forms of bhakti are complimentary. In other words, one may chant God's name or repeat a mantra, but it will not result in God realization unless your mind is in God while doing it. The same thing goes for performing pooja, arti, religious rituals, fasting, visiting holy places, bathing in holy rivers and ponds, reading holy scriptures, listening to spiritual lectures, etc. These complimentary practices are meant to help us keep our mind in God, and they are only valuable on the path of bhakti to the extent that they help us do that. Thus we see that the practice of bhakti is also inclusive, because there are unlimited different ways that bhakti can be implemented - as long as the mind is in God, any other physical form of devotion that you compliment it with becomes effective. There is no wrong way of practicing bhakti, as long as your mind is in God.When we understand these universal spiritual principles regarding God realization and the path of bhakti, then the idea that someone would have to belong only to a particular religion or sampraday in order to reach God becomes unacceptable. All the sampradays that exist within Hinduism have been started in the name of great Saints who taught a particular way of practicing bhakti for the people who lived at a particular place and time. They taught what was most beneficial for those people at that time. All these Saints taught to attach the mind to God and to humbly surrender oneself to God to receive His Grace. The only thing they differed in was which complimentary practice they recommended. Nowadays the people following a particular sampraday may become rigid and think that this way is the only way, and someone who adopts another way of practicing bhakti can never reach God. It is because they are focusing only on the outer practice of bhakti, which is only complimentary, when the thing that really matters is whether one's mind is in God.One should also remember that the path of bhakti is not only universal and inclusive, but also eternal, whereas all the various sampradays are temporary; they began one day and will also vanish one day. They are only the different traditions within the path of bhakti. We should focus on the eternal principles of Sanatan Dharm as they relate to the path of bhakti, and practice bhakti to our chosen form of God, with the guidance of whatever true Guru provides us the most benefit.