According to this table, SL was as I stated, but I have no independent confirmation. Standard 531 was .8 .5 .8. There were variants, such as PRO and ST that were different.
As you point out, 531 was available in many variations. I used .9/.6/.9, at least according to the pamphlet in the box. The "new" SL is .7/.5/.7, but that's modern high strength steel. The original versions of SL and SLX were indeed .9/.6/.9, as can be seen on this
chart. (As well as in the chart you put up.)