At Colgan I rarely ever credit over block. There is nothing fancy about our "contract" and If you are not trying very hard to make extra you will see none.

An example is I am a lineholder:
I want as many days off as possible and I commute so do not ever bother calling me to ask me to pick up a trip (scheduling). Because of this I may block 75-80 hours per month.

Our trips are blocked pretty generously and when we have massive edct times (always) we are aware and typically will not board the plane and subject the pax to a 3 hour sit. Because of this I will get to the plane at noon for a noon 30 departure, have an edct of 4PM so we will board at 3:15, push off the gate at 3:45 and end up sitting for 30 or so minutes more depending on ATCs mood. We fly the flight and end up under block since the company anticipates the delay and the sit so no extra credit.

I deadhead maybe once every 4 months so that half credit is never there

I never ever EVER work on days off so the 3.45 credit is never there

repo credit only happens in ALB and it is 10 or 15 minutes and take 35 so I avoid that like the plague.

MX/WX canx although these are common here for some reason they never come my way.

Holidays, do not usually work them so no 3.45 there

Training (my favorite) I had ground m-f so I bid a line with a trip m-thur. They drop the trip for training (worth 22 hours) and do NOT give me the credit for it. They then pay me 10 hours credit for 5 days of training but since I lost the 22 hour trip I am under guarantee for the month so that month is shot.

Long story short, on average my block vs credit is almost always dead on with the exception of a couple rare hours (less than 5).

That is what a lack of contract can do. Express jet does not have this problem since with little effort many of my FO friends there will end up with MORE days off than they started with and 60 hours block and 85 hours credit all through witchcraft and trickery working the system and their great contract.