Colostrum is usually produced with at least a 2 year sell by time. I always check on buying so it will keep for another year if not used. I'm surprised yours doesn't have a sell buy date on somewhere.
However, it doesn't suddenly go off on the sell by date, and as the packets are sealed and last 2 years+ anyway, it's highly likely it will be effective for another year, even if it is out of date. You could have a look at what Mole Valley are selling now and see if they have plenty of time left on them. If so, the chances are that yours from last year is still in date.
So - it all boils down to - do you feel lucky?
As for your lamb macs - do you really need them for lambing inside? So long as they're not in a howling draft, lambs are incredibly resilient and can stand a lot of cold. I've just had a couple of ewes lamb outside (unexpectantly) on a really cold and windy day. The mothers chose a sheltered bit of the field, and the lambs were up and feeding in no time.