In the Megaman TCG, what does a collector number that starts with "4" indicate?
These cards were misprinted. The set number is supposed to be 3, just like the other cards in the set.

I found this answer in a supplement to the Grave starter deck rulebook titled "MegaMan Trading Card Game - Current Rulings Document 2.0 - 4/1/2005".

The list of cards that were misprinted in this way are:


BambooLance (3U35) 
BugCharge (3U38)
Geyser (3U40)
MagBolt3 (3U42)
Muramasa (3U44)
VoodooDoll (3U46)