Last year around the same time ABCL 0.23 was released. This release featured experimental support for the long form of DEFINE-METHOD-COMBINATION. Last February I started testing our implementation using tests that I found in SBCL's test suite. Unfortunately, I quickly found the implementation wasn't labeled experimental without reason and started fixing the tests one by one.
After other priorities interrupted my work in March, I picked up the remaining work two weeks ago. Today, I committed the last test cases ported from SBCL's test suite. They all work. Particularly hard to get right were the ones involving the (:ARGUMENTS . arguments-list) cases.
With the status that we have now DEFINE-METHOD-COMBINATION (long form) is no longer considered experimental! We're another step closer to full CLHS compliance!