A couple points in nomenclature, Luka:
1. It is acceptable under the rules of the International Code of Botanical Nomenclature (ICBN) that a cross of two species can be designated with or without the multiplication sign (×).
Therefore Lilium ×testaceum could be the same as Lilium testaceum. This is because "testaceum" is recognized as the name given for all crosses of L. candidum and L. chalcedonicum. It is used as a shorthand for writing "L. candidum × L.chalcedonicum". Any botanist learned in the Lilium genus would just know that testaceum is not a species. Unfortunate for us, that we don't always "just know" automatically. Also unfortunately, different authors may use different rules of their own, and it can really get confusing.
The same could be said about Lilium ×elegans and Lilium elegans, or L. ×hollandicum and L. hollandicum.
2. To my knowledge, there is no way to designate whether a cross is naturally occurring or not. Hybrids can and do occur naturally, and are designated in the same way as basic human bred hybrids, unless a specific clone is named. A hybrid is not a true species just because it is naturally occurring.
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It has been proven by chromosome analysis that Lilium elegans is indeed a group of hybrids exclusively (or almost exclusively) involving L. dauricum and L. maculatum, and that the lily described by Thunberg was not a wild lily.
Personally, I don't think the data base here is at all an authoritative source, and as such, we ought to be congruent with one that is. We are fooling ourselves to think that we know better, or have better sources of information than an authoritative source. Changes in authoritative listings that reflect new or evolving data sets are never instant, and I would guess that the CoL will eventually list L. tennii as accepted. The paper you posted about tennii, Luka, has to be reviewed and verified. How do we know if that paper actually tells the truth? Leave the expertise up to the experts. Meanwhile, just realize that no one and no thing (like our data base) is perfect.