China 1940 $20 Type 3, Secret Mark, Unwatermarked, Perf 14 - Blue Threads Or Fibers?

Good Morning,

I haven't got a lot of these to compare and the internet pictures just don't have the resolution that's necessary to see or tell what the paper must look like for this stamp. I have a China 1940 Dr. Sun Yat-sen $20 Type III, Secret Mark, Unwatermarked, Perf 14.

However it appears to have blue threads or fibers both front and back - I would like to know if this is normal please.

Thanks Everyone!

(Just to be more clear - not a blue cancel, they are actually blue fibers or threads on both front and back)

FRONT - SEE TOP AND RIGHT:


BACK - VARIES:

It seems blue or red fibers appeared in some paper sheets used during the war period.Printings in Honk kong for example.Sun Yat-sen, Hong Kong Dah Tung printing,

Thanks Perf12! I may need to pickup some more resources / stamp material... too much variation on each it appears.

Some Added info on the printers.
http://www.stampprinters.info/SPI_c...ry_china.htm
The issues:
http://values.hobbizine.com/chinastamps/1940.html