No other human endeavor erodes more quickly than proficiency with a handgun. It's perishable, it dies quickly. While the basics may remain, the fine edge is easily lost. Less rounds, more practice sessions. When I'm on top my game I can maintain proficiency with a single box of ammo, shot twice per week.
When I'm off my game, a hundred rounds is tiring. I don't believe that you learn much during the second hundred rounds, except muscle memory.