You can't control the small venue prices precisely. (Even Amazon KDP will sometimes lag significantly.)
So you'll never be able to do this perfectly the way one would want to.
You can set the slow ones early and then once they've switched, do the faster sites and announce. (Generally you get so few sales through the slower sites that being on sale unannounced for days or weeks before and after makes no significant difference.)
You can ignore the slower sites and just announce the sale for X, Y, and Z where you have more precise control.
You can announce the sale and mention on your blog/site/mailinglist that some sites may not display the sale price in a timely fashion. Customers who use those sites can contact you directly if they have a problem. (And then, personally I'd just send them a copy for free, but you could make some other arrangement as desired. Contact them when it's available, direct sale through paypal, etc.)
Bottom line, it's a hassle that doesn't tend to be worth it even try across all channels if you're everywhere through aggregators.