The soft top handles were made removable at 250 SL VIN ending in 5089. This is in the list of changes for the Pagoda from Frank Mallory's listing in the Mercedes Collector magazine.
Soft top change is also reflected in the spare parts catalogue, confirming your finding. In addition, some 6 first 280SLs went back to one-piece handles and then as of VIN 000007 to VIN 012192 back to two-pieces ones, to be replaced again by a 107 handles after.
But I am not responding in this discussion because I could not figure out what happened to the hard top handles. Were they replaced at the same moment? No clue. We can speculate that yes, but I am not sure.
All in all my car was ordered without a soft top. One of the POs installed a late soft top with one-piece locks - I am grateful for that! My hard top also has one-piece locks, most likely replaced by a PO as well - and I am also grateful for that! It is so much more convenient! I have read here on the forum that this change was due to safety regulations. It has nothing to do with comfort, I am afraid.
Back to earlier question from Mauro - a set was two pieces as per the parts list.