I tested them all on the HP8405A VVM with the 30pF loading cap and the spread in frequency now seems a bit less.
The highest measured 4.032060MHz (+60Hz)
The lowest two measured about 4.031960MHz (-40Hz)
The others were within 15Hz of 4.032000MHz.
So even the worst one was just about in spec for IQD's 'initial' 15ppm calibration spec (with 30pF loading) and this is after 20 years sitting in a sample bag in a cupboard here
Note that I had to steal the rubber gloves from the kitchen when swapping between the crystals because the heat from my bare fingertips would cause several Hz drift and this would take a while to settle. I tried tweezers and mini grips but this was too fiddly. So I had to resort to donning the Marigolds