The "Bullseye" glass mentioned above would've been produced using the "Crown sheet" method,the glass being blown and rotated to form a large disc that was then cut up into the required sizes ; it was thin,uneven and easily broken. The "bullseye" was in fact the centre of this piece of spun sheet,being the Pontil iron shear mark such as you would find on any early mouth blown article of the same period.
Another type of glass sheet used for glazing of furniture and windows is "Broad sheet" which was introduced c.1618 from Venice ; this was blown glass formed into a cylinder,slit down the middle and heated until it opened up into a flat sheet. It was thicker,more even and smoother than Crown glass,but restricted in size.It can be recognized by slight irregularities in the glass surface ie ripples and bubbles etc.
"Plate glass" is another type of manufacturing process and is far superior to both previous types ; it can be made into much larger,smoother and thicker sized "panes".
Extracted from Glass- M&G Payton 1976. Hope this helps! Best wishes-Urchin.