To put a bow on this, for anyone with a similar problem.
About 7 months after brewing the beer - which was still completely flat in the bottle - I decided to add a smidge ( about 1/16 tsp, give or take) of CBC-1 yeast to the 8 remaining bomber bottles. About 4-5 weeks after that I decided to check out my progress.
I can’t post pix here, but…
I’m back in business. This is NOT a beer for a hot August evening, but it is a very decent Imperial Stout. The sticktoitiveness of this exercise has me quite stoked. Coffee and chocolate flavors abound, Alcohol warmth is the kicker. These are the homebrewing good days. 