? about contract

I just accepted a request to do a 6th edition of a non-fiction book that I've (obviously) done five editions of over the past 17 years. Each contract since the second has been identical in royalty paid and all other aspects. Does anyone ever re-negotiate in such situations?

No, it has been in print continuously for 17 years. Actually, they don't send me a complete new contract, just a few pages with updated due dates for me to sign. All the terms of the previous contract remain the same. I was wondering if anyone re-negotiates any other terms in such cases.

<< Do you have royalty "bumps" for certain sales targets? >>

I have two royalty percentages, with the higher one kicking in at a certain sales target. Here's what's kind of bothering me, though. Reading this site, it seems like some (many?) people's royalties are based on cover price. Mine are not, they're based on the price that the publisher sells it to retailers for. I think. I never really got straight what the hell they're based on, but I know it's not cover price. And it's not just the case with this non-fiction book, it's the case with my recently published textbook, too. The non-fiction is with a moderate-size house, the textbook is with a giant house, if it makes a difference.

Is this something I should be bothered about?

I have never had an agent. I probably should look for one. I have no reason to think that the contracts I signed weren't standard, but truthfully, I wouldn't know.