Beetroot virgin!

If you do thin them, then give them a good watering afterwards, this will help re-settle them into the ground.  Also, despite the given wisdom, the thinnings can be re-planted, watered in well, and will grow to maturity quite happily, just a few weeks later than the original sowing.  I plant where there are any gaps in the row.

Cylindra are a good one to grow for bottling as they have a fairly uniform cross section so provide lots of slices of similar size and are also tasty.  Only one jar left from last year now