That the original sender signed a BIMI-Location header against this spec is irrelevant. It was used for DKIM validation and then thrown out by the MTA.
To me this is a little confusing, as:
The DKIM signature shown in the example only includes the BIMI-Selector header, not BIMI-Locatio
in the Header Signing chapter, it is stating that BIMI-Location and BIMI-Indicator headers MUST NOT be DKIM signed
The example states in https://tools.ietf.org/html/draft-blank-ietf-bimi-01#appendix-C.5:
To me this is a little confusing, as:
BIMI-Selectorheader, notBIMI-LocatioBIMI-Location and BIMI-Indicator headers MUST NOT be DKIM signed