Well I would say the first label is right as Tetrarose flowers from May to June.

I am not familiar with Tetrarose but looking at a few web sites they seem to agree with May to June.

My Montanas flower in the spring and I see specifically my Clematis montana rubens 'Tetrarose' was flowering on the 2nd of May last year when I posted a photo of it.

Thanks for your comments, I think the july - september must be a printing error, { I,ll find out in about 8 or 9 months time}, that,s the only problem with the nursery I go to, most of their plants don,t even have a label, they just have a sign on the bench, ie, Clematis £5-50, but better than paying £12-50 at the big garden centre next door to them, and they,re usually bigger, and better quality plants, thanks again , Derek.