Bale was sold 3 years ago. Yet our net spend each window since then has continued to be very, very low, even in surplus on some occasions.
In reality, signing players like Alli for £5m or Dier for £4m (just two examples from several of that ilk) has played a more significant part. This is because we've gained two players that, if we had to buy two players just as good today, would cost us many, many tens of millions ... which means we've saved huge sums from what our net spend would very likely otherwise have needed to be to end up with a first XI of equal quality.
Bringing players up through the youth ranks has also played a more significant part than player sales. How much would Kane cost us to buy today? How much would Rose cost us today (he originally cost us £1m and joined our reserves and academy)? How much would Walker cost us today (he originally cost us around £4/5m and joined us aged 19)?
And yes, I realise that United "don't operate in that fashion" ... Ronaldo, Beckham and RvN aside. Instead, you've blown vast sums in net terms on additions to Fergie's title winning squad, yet the team/squad has gone backwards at a rate of knots.