@BrentOneill: thanks for the feedback and the idea of adjusting the platform via the 8 fixings… that’s probably what I need to finish the job, since my ‘shimming’ is relatively rough and requires disassembly of the platform for each modification (which in itself shifts the results a bit) - additionally, your method means lowering the platform in the z-axis, mine means raising it, so they ought to be pretty complementary methods 
!
At any rate, I spent some time today designing a better thickness measurement .FORM file - the cube wasn’t really necessary, I decided, since it was the base plate I was after, and it was cheesing me off that I didn’t have any tabs… plus the middle position was also unnecessary. So I made some mini base plates in SolidWorks… the result looks like this:
This allows measurement of thickness on plate (in the meantime, I don’t even bother washing the parts, since the callipers are much quicker and easier to dip in alcohol and clean up) - I measure, record, and bin the parts; If you do rather take the parts off and wash them (don’t let them swell up in the alcohol bath!), seeing as I was making 8 individual parts anyway, I added 1 to 9 dashes per part so you don’t need to scratch an identification number into each part:
Additionally I added an anti-blowout/drain hole on the front-hinge corner:
This 2015_07_27-2cm_base_thickness_plate-x8_numbered.form (2.2 MB) redesigned .FORM file is also quicker to print (only 14 mins with clear on 0.2mm) and uses even less resin (only 4.0ml instead of ~6.5ml, discounting whatever is wasted on the build platform, of course).
I now have all 4 build platforms to a max. difference of around 0.35-0.4mm from thickest to thinnest position, including the bow (on Friday, before I started with all of this, I had around 1.3-1.4mm in the worst case!!!); the z-axis offsets are now all in the -0.5 to -1.0 region, depending upon tank/platform combination. The results are zero dropped callibration parts and no brittle tabs - I get all of the 8 parts off inside about 20-25 seconds, no hammer and chisel necessary, no danger of injury.