says
Shoo...nothing to see here. - zeio
My information is a bit outdated as I'm no longer with my old club.
Custom rubbers were available to the public upon special order. There was actually an information on the Butterfly web site how to order your own customized rubber. Basically, you can choose certain top sheet with certain sponge as long as it's not extreme and spring(or tensioned) sponge. I'm pretty sure you could order one until 2018 but somehow it disappeared from the website in 2019. Probably because of price (more than Dignics per sheet, and with min order qty) and popularity.
As for SP rubbers, what the Sales person of Buttefly said was that it was purely for traceability as they are one of the toughest bunch when it comes to sponsorship and misusage of their product. Most high profile Japanese players visit the factorty to handpick their rubbers but some (and overseas players) get theirs sent. As you know, rubbers vary in hardness even in same model and sponge thickness. It's just a part of manufacturing process because of the inconsistancy in sponge thickness. And sponsored players get to choose the hardest rubber out of the line.
Now, that was the information form around 2016-2017 so it could well be different now especially when Tenergy Hard was available provided to pros before it hit the market.
Found the text (but not URL in Internet Archive, sorry!)
--------------------------------
Q「特注ラバーを作製することはできますか?」
A「ハイテンションラバー以外は、基本的に作製可能ですが、ハイテンションラバー以外でも、一部作製ができない組み合わせもございますので、事前にお問い合わせください。なお、価格は定価の40%増、納期は40日~50日程度いただいております。なお、ご注文は1枚から承ります。
詳細につきましては、お客様サポートセンターへご確認ください。」
-------------------------------
In short, it says the customized rubber can be made with an exception of tensioned rubber. 40% increase from normal retail price, L/T 40 to 50 days, minimum order of 1pc.
It doesn't matter if they stopped offering. The customization is more or less limited to sponge thickness/hardness and mix and matching models within the same series. Just like the custom blade service they offered that was limited to common structures, you couldn't order something like what KLH used.
High-tensioned getting ruled out makes it clear Butterfly acts like DHS and others here. Like I wrote above, something "real custom" like the Sriver + Bryce that only PROS can get, or like CQ's Bryce Speed + Spring Sponge at WTTC 2009.
Last year, a Japanese blogger contacted Butterfly asking why they couldn't list what Harimoto was really using on their official site. The response is "It is very difficult to answer..." because of "trade secret."