If the lines in your file are all the same length (even the blank ones) and each field is also fixed length then you can use the fact that unpack formats ignore whitespace in conjuction with the @nnn absolute position specifier to lay out the format in a manner that is relatively easy to write and later read.

By fixing the start of each line using @nnn and then using relative lengths and xxx to position stuff within each line greatly simplifies working out your format. In the example below, I've left the original 'specification' lines interleaved for readability and then used a regex to strip them out before using the format. There are several ways of doing this, and the much-maligned HEREDOC might actually be a better way. You could also omit them if you preferred.

Using qw// in conjunction with a hash slice to name the individual fields is a nice way of laying out the field names in a clear and concise manner. You can the assign a ref to the hash into another hash indexed by personnel id (or lastname etc.), giving you a HoH which is probably the best structure for this kind of work.

my $unpack_format = 
'
@0  A8      xxA9       xxxxxxxxA8      xxxxxxxxxxxa5
    LastName, FirstName  Home <hm phone>   field <value>
@53 A19                xxxxxxxxA8      xxxxxxxxxxxa5    
    Address1             Work <wk phone>   field <value>
@105A38                                   xxxxxxxxA5
    Address2                               field <value>
@157A4  xxA5   xxA8     xxxxxxxxA5   xxxxxxxxxA5    
    City, State, zip     field <value> field <value>    

@261xxxxxxxA5   xxxxxxxxxxxxxxA5   xxxxxxxxxxxxxxxxA5
    field <value>      field <value>        field <value>
@313xxxxxxxA5   xxxxxxxxxxxxxxA5   xxxxxxxxxxxxxxxxA5
    field <value>      field <value>        field <value>
@365xxxxxxxA5   xxxxxxxxxxxxxxA5   xxxxxxxxxxxxxxxxA5
    field <value>      field <value>        field <value>
';

## remove the "documentation" lines.
$unpack_format = s[^\s.*?\n][]mg; 

my %personnel;

# Assuming that the Personnel number is an integral part of the filena
+me
 
for my $filename ( <PID*.rec> ) {
    my %record;
    @record{ qw[
        lastname firstname homephone field1
        address1 workphone field2
        address2 field3
        city state zip field4 field5 field6
        field7  field8  field9
        field10 field10 field11
        field12 field13 field14
    ] } = unpack $unpack_format, slurp_file( $filename );
    
# Slurp file could be a function or do{ local (*ARGV, $/) = $filename,
+ <> };
# Search for [Juerd]s "Cheap idioms" node for details
    
    $personnel{ $filename =~ m[PID(\d+)\.rec] } = \%record;
}
[download]

However, I strongly suspect that lines like

City, State, zip     field <value> field <value>

nn your specification don't indicate that City is a 4-byte field or State 5-bytes, but that within the overall 21-byte field allocated to them, the parts are variable length seperated by commas.

unpack has no mechanism for dealing with this variable-width-within-a-fixed-length-field type of data. You would need to unpack the 3 as a single field and then use split or a regex to subdivide it later, which is a pain.

In this case, I would probably go for a big-regex, though that doesn't mean it has to be complicated or hard to write. And using the /x modifier and embedded comments, it can become self documenting. Using your record specification as a starting point, and then interleaving the elements of the regex lined up as best you can with those lines makes for a reasonably readable layout. The need to add \s(*|+) between the elements when using /x has the effect of making the regex look 'noisy', but it's a trade off against the self-documentation provided by the embedded comments and alignment. Overall I find this quite readable, but YMMV.

my $re_record = qr[

#LastName, FirstName  Home <hm phone>   field <value>
([^,]+)  ,([^ ]+)   \sHome <([^>]+) >\s+field\s<([^>]+)> \s*\n

#Address1             Work <wk phone>   field\s<value>
(.*)                  Work <([^>]+) >\s+field\s<([^>]+)> \s*\n

#Address2                               field <value>
(.*)                                    field\s<([^>]+)> \s*\n

#City, State, zip     field <value> field <value>          
([^,]+),([^,]+),(.*)  field\s<([^>]+)>\sfield\s<([^>]+)> \s*\n

\s*                                                         \n    

#field <value>      field <value>        field <value>
field\s<([^>]+)> \s+field\s<([^>]+)> \s+ field\s<([^>]+)> \s*\n

#field <value>      field <value>        field <value>
field\s<([^>]+)> \s+field\s<([^>]+)> \s+ field\s<([^>]+)> \s*\n

#field <value>      field <value>        field <value>
field\s<([^>]+)> \s+field\s<([^>]+)> \s+ field\s<([^>]+)> \s*\n

]x;

my $record = slurp_file( $filename );

my %record; @record{ qw[ .... ] } = ( $record =~ $re_record );

$personnel{ .... } = \%record;
[download]

You could use a repeat count for the last 3-lines/9-fields, but if the data has a fixed number of fields, I think that using cut&paste makes things clearer in this instance.

One tip: If you decide to go the 'big regex' route, start by commenting out everything but the first line, capture to an array and print the results. Once you have that capturing the right things, uncomment the second and repeat. Simple advice, but it took me a while to work it out.