Yes it's accrued seasons. Credited is for pensions/benefits etc. They can be different.
The CBA language is weird about the 6 game criteria.
Here is an article AFTER the new CBA from last year.
https://www.nfl.com/news/2020-nfl-free-agency-glossary-all-the-terms-you-need-to-know-0ap3000001106817
Accrued seasons: Used to determine a player's free agency status (unrestricted, restricted, exclusive rights). In order to accrue a season, a player must have been on (or should have been on*) full-play status for at least six regular-season games in a given season. A player under contract must report to his team's training camp on his mandatory reporting date in order to earn an accrued season. If player holds out his services for a "material period of time," he is also at risk of not accruing a season.
*When I write "or should have been on," note that this is the language used in the CBA. Basically, in order to accrue a season, the player needs to be on the team's active/inactive list, injured reserve or reserve PUP for at least six regular-season games in a given season.
I believe (and as you said unless someone has better facts) that the 2020 CBA changed what the previous CBA's criteria was.
Kumerow has 3 accrued seasons because he was on IR in 2018 with GB along with his 5 games.
One way I believe this is true is Hodgins was on IR all last year and still has an accrued season. I don't think he would of got that with the old CBA.
The source I use for accrued seasons is OTC. It shows Kumerow with 3 and Hodgins at 1.
Other sources show conflict with this but I use OTC and I haven't seen a situation where they were wrong YET.
FWIW.
https://overthecap.com/player/jake-kumerow/4455/
https://overthecap.com/player/isaiah-hodgins/8947/