Now I see what you mean, equal drift rates but different up-time. Assuming two clocks coming up at different points in time this will indeed cause time differences if they are initially synchronized with a third clock. If the clock coming up later synchronizes with the other clock already running there should be no issues though.

I read the article, too, and this two different ways of converting are more or less equivalent of two clocks starting in sync but drifting relative to each other. Therefore my initial comment was quite on the spot.