I think the packaging advice is meant to be interpreted with a degree of gardening experience. So for instance, last year, when winter went on for weeks and weeks, and there wasn't a hint of spring till April, some of the seeds that claimed to be plantable in Feb and March, really shouldn't have been planted. On the other hand this year, so far, a February or March planting might do well (obviously we don't know whether Arctic conditions will appear in a fortnight, and having seen snow in May one year, I am surprised by very little). But you have to see the planting instructions as a broad guide, so that when it says 'plant outside Feb-April' what it actually means is that if you plant in Feb, and we have a mild year, you might just get away with it, so why not give it a go? You have to go with your gut. I got my potatoes in early this year cos I have a gut feeling that the weather pattern of a mild spring is not going to change because of the jet stream, BUT I could be looking very stupid in a fortnight and doing a lot of things with fleece!!