Yes, it can easily happen. Weather changes can affect all plant types and classes causing "repeat" flowering "out of season". Any time the weather conditions appropriately mimic those required for flowering, it will happen. I had a client in Pacific Palisades, CA who filled her yard with O'Neal blueberries because the climate there triggered them to flower and fruit for nearly nine months of the year. Her three year old daughter was WEIRD for blueberries so she wanted the little girl to have those memories. Banksiaes flower spring through nearly fall along the coast in much of California due to the climate. They and Fortuniana flower February through late September here in North Santa Barbara County. For many years, I was only able to gather pollen from Gallicas planted as new bare roots as they received sufficient "winter" in cold storage and even their new growth produced blooms. We mark plant performance by the calendar. Plants perform based upon whether they receive all their resources by whether their thresholds are met. They don't have watches and they can't read. If they get what they need, they will do what they are "told" to do by what they've received.

That is really interesting — thank you, @roseseek.

My daughter noticed a typically once-blooming 'Seven Sisters' with some scattered blooms on it just last week in Kensington in the East Bay.

How cool!

I have several Glenn Dale wichurana climbers, and it's not unusual for them to produce a bloom or three in the Fall, especially if there are weeks of alternating warm/cool/warm temperatures. I take them for what they are, just welcome outliers,

How neat, John! I planted Silver Moon free standing in the old Newhall garden where it grew for 18 years. Once it reached "mountain size", it frequently went through several "flushes" of bloom many years. Maturity and alternating warm/cool to cold periods do wonders for "tricking" plants into repeating their performances.