Inconsistent Offers of PRI Date

My starter for ten is that I appreciate that the CEng PRI process is volunteer driven (and I volunteer for the IET in a different capacity).  My question centres on why the offer of a PRI is so inconsistent. 

My application was submitted in July, so I am now at the end of the 20–22-week approximate timeframe stated in the Application Acknowledgement and 3 months from passing the Pre-Interview Assessment Panel.  But here is the source of my query; a close colleague submitted their application after I did, passed their Panel after I did and has already had their interview.  Note that we are in the same industry/company/team, so I would like to understand the delay.  Is it really down to finding appropriate persons to match the specific evidence on my application?

I have tried the obvious and am quite aware that this is a frequently asked question on these forums, but the inconsistent nature of the process is starting to have an impact.