Always good to see more from Farthing
As to sausages, I'm not convinced. Slinn only records 1492 as receiving Harris branding before 1927. That was in 12/24, and I do wonder whether that is a typo as the others on adjacent lines are 12/34. In general, the Harris branding appears to have happened in the 30s as noted on p48.
Assuming that Slinn's dates are those on which the branding was applied, rather than just a date on which it had been observed, then I reckon Mikkel is quite safe, at least until March 1929
Nick
ps. Now look what you've done! The binding on my copy has started to give up and pages are falling out. Must take less interest in Siphons