According to Jane Straus, the author of The Blue Book of Grammar and Punctuation http://data.grammarbook.com/blog/hyphens/hyphens-with-common-prefixes/ (http://data.grammarbook.com/blog/hyphens/hyphens-with-common-prefixes/):
"Generally, with common prefixes, you do not need to use a hyphen unless it would avoid possible confusion."
I recommend that the 2017 rules consistently use the terms preflop and postflop without hyphens and all-in with the hyphen.
Regards,
B~