Offers do come after binding agreements are signed. For example cast back 6yrs when TPG inked a deal to buy iiNet for ~$1.4bn only to be forced to raise that offer after M2 lobbed a competing one. Ultimately TPG succeeded buying iiNet for just shy of ~$1.6bn.
https://www.crn.com.au/news/m2-offers-16bn-for-iinet-bidding-war-starts-403217