Cannot mount an older disk

[Mikhail T.]

Hello!

Going through older hard drives, I found one that still seems to work 
and was curious, what's on it. The OS -- 12.1-STABLE -- sees it find. 
The disklabel seems sane (except for the number of partitions):

    # /dev/ada1:
    8 partitions:
    #          size     offset    fstype   [fsize bsize bps/cpg]
       b:   12582912          0      swap
       c: 1465149168          0    unused        0     0 # "raw" part,
    don't edit
       d: 1452566256   12582912    4.2BSD     8192 65536 52352

and there are ada1, ada1b, and ada1d entries under /dev. So far so good. 
Unfortunately, both mount and fsck tell me the same blatant lie, that 
the device does not exist:

    # fsck -y /dev/ada1d
    Can't open /dev/ada1d: No such file or directory

    # mount /dev/ada1d /mnt
    mount: /dev/ada1d: No such file or directory

Any suggestions? Thank you! Yours,

    -mi