The year was 2009. The first of the very
very cold winters in this region. -21C on 15th December it was, and the snow stayed for about 6 weeks.
11th May 2010 and, lambing finished, BH and I were off to an auction. Passing the field where our (untupped) shearlings were, BH said, "Oh! We've got a lamb!"

Mum was with lamb, all looked well, we continued to the auction.
On our return, off to see the new arrival.
Eleven lambs. We found 10 mums, all happy with one lamb, so I had a new pet lamb

- and we had 10 new mums

No other shearlings produced, of the 60-something in total that we had that year.
We worked back and realised that they'd have been tupped on 15th December, that very very cold day. Well we already knew we'd had a wether in that batch as he'd been identified and sold in the spring. So now we wondered whether that wether had actually been a rig...
Then one of our neighbours, who run rigged wethers as teasers and then leave them with the flock over winter, reported a similar batch of lambs on 10th/11th May...