Derek Broughton wrote:

... the 23W CF really was approximately 23W but the 42W CF was much less.

Surprising...

... did you check the lumen output either by using a standard candle,
or a photometer (perhaps one in a camera?).

No. I'm not sure how standard standard candles are.
I've used CSA standard fingers...

Don't CFs dim with age?

I believe they do.

Can we then expect the relative efficiency to improve over time?

I doubt that. Don Klipstein might help here.

Nick