This is an FYI only, the issue is resolved as noted below.

User PC's on several subnets were not getting SLPDA info though DHCP as
configured while one subnet was working fine. This was verified on the PC's
with slpinfo /a.

I ran a packet capture of a PC and manually executed a dhcp release and
renew on each of the non working subnets and the working subnet.

In comparing the packet captures between the three subnets and focusing in
on the DHCP process, I found the following. In all DHCP subnet
configurations, the DA was set and flagged as mandatory. The Mandatory flag
normally tells the PC to overwrite any DA settings that are configured
locally. The only difference between the DHCP Packet captures is in the
actual value of the Mandatory YES field. In the capture of the non -working
subnet DHCP request/reply, the Mandatory YES value was 144 or 90 hex.
Capture excerpt
SLP Directory Agent Option (78), Len: 5
Mandatory Flag: Yes (144)
IP: 10.x.x.x

The working subnet capture the Mandatory YES value was 1.

Capture excerpt
SLP Directory Agent Option (78), Len: 5
Mandatory Flag: Yes (1)
IP: 10.x.x.x

My conclusion is that the PC Client was disregarding the SLP Mandatory
value of 144 and thus the DA as well.

Resolution: This forum had a posting regarding that was not even remotely
close to the issue I had BUT, did provide the notion and in the end the
resolution. Using a newer version of DNSDHCP management console I toggled
the DA Mandatory setting between NOT Mandatory and Mandatory and saved the
change. This reset the value of the flag to 1. It seems that there may be
a difference between the acceptable hex values of SLP mandatory setting that
the old management console set and the 4.9 client family accepts.