Sometimes, I have mixed results when trying to tag companies or organizational accounts in my posts. I enter the @ and start typing the name of the company. Short or easy names usually authenticate. Longer names with multiple spaces seem to pose the most difficulty. Looking for a secret way to guarantee results. I have even tried to enter the numeric value for the company in my post window and that does not work. Right now, working on tagging on Women in Defence (yes defence) Technology in one of my posts and I cannot get the link to resolve.
I believe this is a LinkedIn API limitation since the search populates whatever Linkedin returns back to us. I've seen in other posts in the forums that adding underscores "_" in between words of a long LinkedIn page name would yield more favorable results, so if you're looking to tag/mention "Women in Defence Technology", perhaps try "Women_in_Defence_Technology"