In those days the "number cards" were peel off stickers. It is entirely possible that a number card was issued by itself to reflect a new number and pasted on an existed phone.
Customers certainly moved around hard wired phones after divesture.
Also, in those last days I don't think they were as strict on number card use as in the old days. I saw a great variety of newly installed number cards--some ANC, some with 2 letters, some with the full exchange name. It's rare, but there were the rectangular cards (for Touch Tone phones) that had the full exchange name spelled out; squeezing DEvonshire in that little space was quite an accomplishment.
In the 1950s sometimes they used a fancy card in which the installer had little numbers he put into tiny slots on the card face. These were black background with white numbers.
In the 1960s we got a peel off sticker with our area code which was to be pasted on the phone dial, overlaying the "wait" as in "wait for dial tone". If they had to do that today every time an area code changed they'd go broke just from postage.