Although this is an old post, I just wanted to say that the conclusion reached seems incorrect--more than one recessive/dominant gene is not necessary in the seed parent to give that ratio of remontant seedlings. Since the seedlings arose from open pollination, there was no control over the source(s) of the pollen, so you do not know how many pollen parents were involved. All seedlings resulting from the pollen of a homozygous once-bloomer (containing only the allele that causes once-flowering) would themselves be once-flowering. As such, it is more likely that your plant was pollinated by at least one rose that is homozygous for once-flowering behavior (if diploid) in addition to at least one rose that is not. Because the seed parent is most likely diploid, it is probable that the offspring of any controlled crosses of this variety with a repeat-blooming rose would have been about one-half repeat-blooming. A 1:12 ratio of remontant seedlings could be explained if up to around 4 in 24 ovules were pollinated by homozygous repeat-blooming varieties (since about 1/2 of their resulting seedlings, or 2 in 24, would be expected to be homozygous for repeat bloom), or that up to 8 in 12 ovules could have been pollinated by varieties that were heterozygous for flowering behavior (of which only 1/4 of resulting seedlings, again 2 in 24 overall, might be expected to be remontant). The remainder could then have been pollinated by varieties that were homozygous for non-remontant flowering to give the final ratio.

To find out whether there are really multiple genes involved (although there is much evidence to suggest that is not the case with diploid roses in sections Synstylae and Indicae), you would need to employ careful emasculation and deliberately pollinate with pollen from a single variety that could give a clear answer.