Does "simplification" relation reflect "traditionalization" relation in Unihan?
Let me summarize the cases and try to answer your question (TC = Traditional Chinese character set, SC = Simplified Chinese character set).

Some characters were never simplified. For example, 井 U+4E95 is in TC and in SC (and for that matter, most characters). In the Unihan database, codepoints like these have neither a kSimplifiedVariant nor a kTranditionalVariant (both fields are empty).

There is a traditional version of the character, only present in TC. For example, 書 U+66F8 is in TC (and not in SC).  The kSimplifiedVariant of 書 is 书.

The is a simplified version of the character, only present in SC. For example, 书 U+4E66 is in SC (and not in TC). The kTraditionalVariant of 书 is 書.

The character is used in both character sets depending on context. This is a bit of a mess, and I've written more about it here


The relations should &quot;reflect each other&quot;, but they're not a bijection
It should be the case that if X.kTraditionalVariant includes Y, then Y.kSimplifiedVariant includes X. When I last checked the data about a year ago, there was at least one bug where that wasn't the case.
This does not mean that the relation is one-to-one or onto. There are some cases that are truly bizarre; check this out here for all of the weird cases