Hi,
I come from a HR background - in Australia, but have some tips.
Grading is fine - it's like recruiting anyone - there are some candidates that will not progress past the submitting an application. Check how long you are legally required to hold any applications (to protect against discrimination claims - here I hold for about 6 months), and then feel free to securly dispose of the applications!
With older information, do you have capacity to scan older documents and store them on CD in the file to control the paper volume?
I'd highly recommend talking to your company about getting an electronic application/candidate management system. We used a HR/Recruitment one, but there's bound to be a agency candidate management system or two out there. It is a significant initial outlay which won't be palatable in this climate, but when my old company went that way, it was an absolute God-send and worth every penny ten-fold (if only for our sanity!!). Ours was a good 6 month process of researching options, then designing the system to our needs, then training to going live.
ALL documentation is stored electronically - applications are by a link to the program on our website so they come in electronically, all letters, references, the LOT are scanned and stored electronically. It tracks what jobs people apply for, how they progress through the process, what the outcome was. Were they unsuccessful, but marked as worth keeping in touch with? And it did away with paper files, completelly!!
The outlay may be scary, but counter to the intial cost, there will be savings in the time it takes to track candidates, and probably increase the agency's capacity to handle more contracts and candidates. Many programs you should be able to start with a basic system and the build as you needs/ability to pay for it increases.
I'd put an expiry on any candidates, ie you have to be in touch every 6 months to keep 'hot'. 'Warm' is for 12 months and then anyone older than that needs to re-apply. A) you have current information, B) if you go electronic, you don't have to enter that detail- they do it for you!
Good luck.