All the products that WESTERN ELECTRIC manufactured always had a model or type number. The 66 series connecting block was the first IDC type connecting block in the BELL SYSTEM, introduced in 1962. It came after the 65 type. Some of the block series types are:
66A1-25, 66A2-25, 66A2-50
66B1-25, 66B4-25, 66B4-25C
66B3-50
66C1-16, 66C2-16, 66C2-32
66M1-25, 66M1-50
66E3-25, 66E4-25, 66E8-25
The number does mean a specific block arrangement or config in relation to the contact make up, etc.
The 110 connecting block system is an update to the original type 88 connecting block that the BELL SYSTEM introduced in the late 1970s. They wanted a more compact and reliable connecting system for phone systems.
In 1979 the type 88 was not the only connecting block system introduced to telephony, the BIX cross-connecting system from Nothern Telecom thru Cook Electric in the US and one from 3M, but I don't recall the name for it.
Hope this helps!
....JIM....