I've never heard of pitching a 2nd round of yeast, unless the fermentation got stuck (stalled). And that's an uphill battle to get that going again, given the hostile environment you pitch into.
Are you perhaps referring to adding yeast with the priming solution for purpose of natural carbonating during bottling? That would indeed be necessary after such a long time of aging, and being a strong beer. Priming sugar and yeast can also help when kegging to prevent oxidation from oxygen that got introduced during transfer. Best it to 100% liquid pre-purge the keg, and use a (near) closed transfer if possible.
Is it done? Have you taken a gravity sample at some point?
I'd say it's ready to keg, you can always age it longer in the keg if need be. The plus on keg aging is you can purge the headspace to prevent oxidation.