Is this true...???

[lammy]

The British Mark I has a rubber ring sometimes called a doughnut sewn between two pieces of wool in the base of the helmet dome. The doughnut was added for the wearers comfort. It was undoubtedly a welcome relief from having the helmet constantly bounce up and down on the top of the wearer skull while running across no man's land. Early Mark I helmet initially had this feature only to be discontinue in mid 1916. The ring didn't stay gone long and was brought back in 1917 no doubt to the joy of the average Tommy.

[lammy]

From here, and if so where does this info come from...???

Helmets and Things: The British Mark I Brodie & the U.S. P17, know the difference

[aef1917]

There is no such thing as a P17 helmet, so any information included in that should be considered suspect.

[lammy]

Thought as much, doughnut should be 1917.

[William1]

I think the error in that article - and it definitely is an error - might have arisen because raw edge helmets continued to be relined throughout the war including with the doughnut liner, which the writer has mistakenly assumed is the original liner.