Yes, you will have to wait until it flowers, unless it has a very distinguishing leaves, but that would only break it down a bit. As soon as it is identified you will know what pruning group it is in. Clematis is tough, if it has 8 inches of new growth it will be fine. And.... clematis takes alot of patience.

Essentially, yes :-)

If you are really familiar with the genus, you can often sort the vines by pruning group based on foliage. But the best way is to wait until flowering. Flowering before May is group 1, flowering May-late June with a typical repeat flower in late summer is group 2 and initial flowering after the end of June is a group 3 vine.

Growth appearing only at the tip of the vine sounds much like a group 3. These bloom on growth produced the current season and if left unpruned, growth will be very high on the plant.