It is interesting that despite its high % of nucellar seedlings, Swingle has several recognized variants now. When growing Swingle from seed, I have seen maybe <5% off types, and only found one worth keeping based on my selection criteria.
The Trifoliate Orange and Australian citrus like Finger Limes are especially valuable for breeding HLB-resistant varieties. Sun Dragon is a noteworthy one with navel-like fruit that have a tasty orange/pummelo-like flavor from what I have heard. It is 12.5% Trifoliate Orange since one of its parents was US-119.