A fill shot for evening league is not uncommon no matter what organization the house is affiliated with. Private centers do this as well. In fact, up until a few years ago, centers only stripped once a week! How difficult do you think it was to find a shot then? But people did and people averaged over 220, if they were good. So its not impossible. You are just expecting too much in having screaming backends at your disposal every week. Now there is a large proportion of bowlers that HATE screaming backends. They find them hard to contol and hard to bowl on. Generating complaints to the center. Therefore, the center may NOT want to provide fresh backends for their evening leagues.
Deal with what you have and put away expectations from your head. We have lots of elderly folks too and they bowl all week every day in the afternoon filling the 32 lane center. Then on top of their play we have two weekdays of 4pm Junior bowlers. So on those two days you can imagine how the fill shot ends up for evening. And people still bowl well, still adjust.
Erin