I have also seen a similar change in an (alleged) sport. Some years ago, I bought a body bag of 'Royal America', sport of 'America'. I was at the time also growing the sport parent. RA showed growth and habit identical to 'America', but the cream colored flowers opened in a kind of globular, cup shape, not at all like the flatter 'America'.

RA is no longer in commerce, which is a pity, because I found it an excellent pillar type rose. I think the sport may have been found by a wholesale company, which propagated and sold it for as long as the patent lasted.

The choices for ramblers in the cold zones are somewhat limited. I have had good success with the Ayrshire group. Those do indeed ramble, everywhere if you let them. The blooms are white and pretty, but lack the lavishness of the Barbier roses. I think Roses Unlimited has one or two, some years. The Damask, Celsiana, should probably be thought of as a rambler. It throws out 15' canes. Then there is Lilian Gibson, which is huge, and will shade out anything growing beneath it.

I gather Dorothy Perkins and sports can be grown in 5. I have not attempted them. Among modern, repeat blooming ramblers, I have Alba Meidiland, IMHO one of the finest of modern introductions. It is hardy for me, but remains bushy.