During my successful transit of the Southend zone on Saturday I was passed over to Southend Director on 128.950 which I wasn't expecting as it's not listed on my PLOG (Radar, Tower, Approach and ATIS are listed).  Unfortunately this resulted in a rather audible sigh from Southend Radar when I asked for them to repeat the frequency. 
Should the frequency have been on the PLOG?

Thanks, Dave