Typically for matches Chase requires you to meet the additional spending but Citi does not. In the case of Chase, they require you to meet the new min spend and then issue the award. In the case of Citi they issue the matching points separately from the actual bonus. For example, if you match from 65k to 75k, you actually get the additional 10k points regardless of meeting the minimum spend for your offer. The spending for your 65k offer remains the same at $4k. Likewise, if you're on the 50k for $3k offer you keep the $3k spend regardless of what you match upwards to.

The min spends are:
$3k for 50k (was 60k recently) public offer
$4k for 65k targeted offer
$7.5k for the 75k Plat Exec but no known 75k plat select - confirmed that they have allowed 60k and 65k Selects to match up to this - I believe unconfirmed if they have allowed the 50k offers to match up, probably because the decrease down to 50k was more recent and most people matching had either gotten the 60k public or 65k targeted offers

I've been using the 65k mailers right now even though they expired so I'm not able to confirm yet if 50k->75k is possible but did have a friend just get one yesterday so he should be trying shortly.