Need To Identify Production Year

Hello. I found that these stamps were produced in 1913, 1915 and 1918. They have the same perforations and same watermark. How would it be possible to get the year of production of each one? The top one is lighter than the bottom one but with very heavy cancellation.
Thank you.

I think the frame size is a bit bigger in the 2nd De La rue printing.

Shade difference in the 2 examples is quite notable.

Here are my notes which come from the Stanley Gibbons 2013 Catalogue.
The measurement is the design size, not including the border.

Waterlow Printings measure 22MM high
2/6 Deep Sepia-Brown - Waterlow Printing - 1913
2/6 Sepia-Brown - Waterlow Printing- 1913

De La Rue Printings measure 22MM high with patchy, yellowish gum
2/6 Deep Yellow-Brown - De La Rue Printing - 1915
2/6 Yellow-Brown - De La Rue Printing - 1915
2/6 Pale Brown - De La Rue Printing- 1915
2/6 Sepia - De La Rue Printing - 1915

Bradbury, Wilkinson printings measure 22.75 - 23MM
2/6 Olive-Brown - Bradbury, Wilkinson Printing - 1918
2/6 Chocolate-Brown - Bradbury, Wilkinson Printing - 1918
2/6 Reddish-Brown - Bradbury, Wilkinson Printing - 1918
2/6 Pale Brown - Bradbury, Wilkinson Printing - 1918

2/6 Chocolate-Brown - Reengraved - 1934
The reengraved issue has diagonal mesh lines by the King's portrait.
instead of the horizontal lines found in the earlier issues.