I have searched old posts, Pre-negotiated deals and even signed contracts but there is no consistency on which MBFS incentives are taxed and which are not. Can anyone with more experience please clarify?
So far, my understanding is:
MIB/Fleet is just subtracted from sale price, no sales tax.
Conquest via Upgrade Certificate maybe taxed?
@trism mentioned conquest is not taxable in this post. But I don’t have any personal experience with that.
Are you noticing a variation in tax treatment with MB leases in CA, or MB leases across the US?
Generally, if the incentive is to the dealer and has the effect of the dealer lowering the selling price, it’s not taxed, but if it’s deemed to be a third party paying part of the lease cost on behalf of the consumer (mfr incentive to consumer) it’s taxed.
I noticed with my Wagoneer S (CA lease) last year that the dealer baked the value of the BEV coupons into the dealer discount (so not taxed) while Wagoneer S leases I saw from other states showed the value of the BEV coupons presented on the agreements the same way as consumer incentives (and therefore were taxed).
Yes, the taxation seems to differ from state to state as well. With some CA taxes being 10%, it is changing the numbers by a few hundred dollars between different offers.
Based on my limited sample / experience, I would expect some variability from state to state, what I was (clumsily) asking is if you noted differences within CA also. 
Yes just confirmed that there are differences within CA also.
The most recent deal posted on Signed has $1500 in the rebates section. That may have been the MIB or Conquest certificate.
A friend signed one yesterday with MIB and Conquest - Was expecting rebates to be listed as $3,000 but somehow dealer listed $542 as the rebates.