I imported a lot of sanderianum from Malaysia, in several batches ( with CITES... straight from Sarawak), and bought quite a few here and there, usually blooming size plants or divisions.
Regarding the seedlings, some are of genuine parentage, some are obviously not. I remember a thread where ( I think Lienluu???) posted a pic of a 'division' of a 'selected sanderianum', that obviously was the standard, crappy form.
In my experience with those plants, there are about 3 groups of plants, that heavily depends on the colonies they are coming from.
Sanderianum lowland type such as Shin-Yi ( that's a famous one), they have darker green leaves, and can reach the size of a kolopakingii, 3-5 flowers, usually the petals are over 65 cm. The leaves can be quite narrow or wide actually, it is an individual variation.
I have got an individual ( I have to find back the pictures) with 120 cm petals in Sarawak, I bought it in bloom, it was obviously a very, very well grown plant for ages. I went at the blooming season, ordered a CITES some months before, and selected in a large nursery that had some hundreds plants in bloom. They tend to have softer, thicker and darker green leaves. The habit stays when they are cultivated. That man grew them in plain big pieces of charcoal, daily watering, and powder fertilizer by the tablespoon at the base of the plant...
Sanderianum highland types, they usually are more yellowish plants with darker colored flowers. The petals tend to be shorter, in the 50 cm+. They are easier to grow as well, because at the repotting time, it is quite difficult not to break many roots on a sand, and a lowland form resent being repotted if it is not very carefully done, and no root damage should occur, or dehydratation will follow. Whilst the highland type has shorter petals, I like it a lot, because the dark ones are very beautiful.
Sanderianum crappy types. Whilst I know the sources for the two former ones, I do not know the exact source for those latter ones. They appear everywhere worldwide, have been used to make a lot of flasks, the petals are in the 30-40 cm, it is hopeless to expect them to go past 40 cm anyway... Usually 2-3 flowers per stem. That's most of the 'blooming size' sands on sale from Taiwan. They occur apparently in much larger colonies, I have seen up to 2000 wild collected plants at once, and the leafspan is about 40-50 cm, yellowish leaves. They tend most of the time to be single growth or at most 2 growths. In Peninsular Malaysia, it is possible to buy those for US$10/plant maximum.
I am very reluctant to buy sanderianum seedlings like that, I would not touch the ones coming from Taiwan, because some looks damn funny compared to the parentage ( lowland parents, and highland type seedlings...).
Now another option that I am quite sure about is that quite a lot of sands 'seedlings' around may not be sanderianum too. Some seedlings prove to grow in a quite odd way compared to mature, bloomed, confirmed plants...
