The $8,500 discount/rebate is actually for purchases, with GM lessees eligible for the extra $1,500 loyalty incentive. But I believe lease incentives also total right around $10k, so manufacturer incentives are pretty much the same, purchase or lease.
People that had a GM Card should also be eligible for an extra $1k discount in the form of GM card rewards. So someone that is a GM lease holder and had a GM card prior to 31 Dec is eligible for up to $11k in incentives BEFORE whatever discount they can negotiate with the dealer.
If you could negotiate a $5k dealer discount (I've seen that much advertised in online ads for at least Premiers), that would be $16k off MSRP before the $1,875 fed credit and whatever local incentives are available. In MD, a MSRP $44k loaded Premier Bolt after ALL discounts/rebates/tax credits/state incentives, we're talking driving off the lot in a MSRK $44k 2020 Bolt for less than $24k OOP before taxes!