The Lambert Sales Co. pre-affixed security issues on their shipping labels, then affixed to their parcels. They were able to determine the amount of postage required per double parcel shipment by using the same type of weighing scale used at the Manila Post office.

In rare instances the parcel weights obtained at the Lambert office and at the Manila Post Office did not tally to which additional postage was required. Inasmuch as there was no longer any space for the additional postage on the shipping labels post office clerks instead cancelled the stamps with blue crayon to denote pre-payment of the additional postage.

Another explanation on the blue crayon cancel is that the stamps were affixed on the parcel package and cancelled with crayon. To me this does not hold water. The idea of postal clerks using regular postmarks and killers on stamps affixed to the labels and blue crayon to those on the package itself does not make sense at all. 

The third and final explanation one came up with is that the stamps were affixed to the package wrapper which were not cancelled by local postal clerks and cancelled in blue crayon upon arrival in New York. The more this does not make sense. Stamps sales was a big source of revenue for the Insular Government. Postal clerks were given strict orders to make sure that all stamp frankings were properly cancelled. Finding one uncancelled stamp on cover during the USPi period is like looking for a needle in a hay stack.