Whistling Pops, I'm not aware of any listings anywhere about dating a Sweet instrument based on the serial number. Maybe you could contact the folks at Sweetheart and ask nicely if they could tell you when it was made. Wouldn't it be cute if it was made in March of 1958?
But I think they didn't start making instruments until maybe the 1970's, ICBW. I'm not at all sure when wooden whistle production began.
I've had a couple Sweetheart whistles in the past and I recall the serial numbers on mine being higher than yours, 3000-ish (could have been 300-ish memory being what it is) and bought in the late 90's. Maybe we could zero in on a rough date if folks here have Sweet whistles with closer numbers to yours. The serial numbers on mine had no letters just the numbers if I am remembering correctly. And mine were bears to play above the second octave D with lots of push and air velocity needed to get to the high a and b. Mine had red thread (cotton?) on the tenons but yours it could have frayed and matted to look a bit like felt.
Whistling Pops wrote:
Does it matter if this whistle is left together or should the head and body be separated when not being played?
You might want to dis-assemble the wooden whistle after playing and swab out the bore too. And it's a good idea to oil the whistle occasionally to keep it in good shape. Sweetheart has care instructions on their site.
Hope that helps.