This is a Type 5, made between 1899 & 1900 (How
can he be so accurate? I hear you mumble)
Read on....

The Stanley No.19 Block Plane is 7” long with a 1 ¾" wide cutter, 1
5/8"
after 1909.
It was first offered in Stanley’s 1888 catalogue. The blade was Fully
adjustable both laterally and depth wise, also the mouth is adjustable
for fine or course shavings.
Everything Exactly The Same as The N0.18 except, this one is 1" longer.

So, "How does he know?" Well, Stanley left lots of clues
in their improvements and changes to their planes by patenting them. These
patent changes can help pinpoint accurately, the period of manufacture.
Sometimes the changes were so close that a particular type was only made
for a very short time as with this one, a 1 year production, then... all
change, again!!
Before anyone asks, No! I'm not going to list
all the changes to all the planes and list all the types.
That would require another web site and would take an absolute age.

Here you see the patent date of Dec. 28th 1886
on the knuckle cap. This Patent
date disappeared from the knuckle cap in 1905 with the type 8. Same applies to
the No.18.