I figured it out one day, if you were to collect every variation of the Six series DA revolvers, it would be over 100 revolvers before you had most of them.
For example, with the Security Six alone, there's the early "low hump" models, the early fixed sight "pre Service Six" Security Sixes, then the light barrel, unscalloped recoil sheild, in all 3 barrel lengths, then the "transition" scalloped, HB models, then the later models,the rare Machined heavy Barrel, add in all of those barrel lengths, in blue and stainless, that's over 20 right there. There's also the very rare .38 Special Security Sixes, MUCH rarer than the .38 Service and Speed Sixes.
There are some rare variations, collecting the DA Six revolvers alone would be a lifelong pursuit.