The initial deal was inked on December 4th of 2017
Post# of 75001
Anyhow, a company is not required to report all material events by filing an 8-k. Only certain events require that an 8-k be filed, such as anything affecting shareholder's rights, failure to meet listing standards, etc. A press release is sufficient in most cases to inform shareholders of materially significant developments such as the transaction they just shared in a PR.
Here is a link which may answer some of your 8-k questions. The thing to remember is that companies will often use an 8-k even though not required, and very often they'll use an 8-k to communicate important information to shareholders in lieu of a press release. https://www.investopedia.com/terms/1/8-k.asp