From https://drafts.csswg.org/css-anchor-position-1/#fallback-rule

If multiple @position-try rules are declared with the same name, the last one in document order "wins".

This section should probably be written to be less absolute, since presumably if @position-try is inside another @-rule (such as @media, @container, @starting-style) we don't want the last one to "win" if it shouldn't actually apply.