In GE Fanuc part numbers, the last alpha character is the revision level. If you order an IC693MDL646 from your distributor, you will get whatever revision level they have available.
Occasionally, there are issues with an old revision level of a module not being compatible with a newer revision level of CPU. GE Fanuc publishes (at tleast tey used to) a compatibility chart that covers those details. In the specific case listed, there are unlikely to be any compatibility issues since the moduel in question is a simple DC input card with a fast filter time.