It is said many words here http://www.unicode.org/reports/tr38/#SCTC about kSimplifiedVariant and kTraditionalVariant field cases (5 cases). But I didn't understand, if these two relations reflect each other? For example if A is simplified version of B, then does it mean that B is traditional version of A?
Let me summarize the cases and try to answer your question (TC = Traditional Chinese character set, SC = Simplified Chinese character set).
The relations should "reflect each other", 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