There are several typos and contradictions in that article. If you read the whole article it also says the 28 gauge size was introduced in 1970. The use of mahogany stock was not uniform either.
For your info, you can see the errors:
1970
Remington introduced a Model 1100 20 gauge Lightweight Field Gun which was built on a smaller 28 gauge frame, and had a lightweight checkered mahogany stock and fore-end. This gun was available with plain barrel ($179.95) or vent rib barrel ($204.95), in full or modified chokes 28" in length, or improved cylinder barrels 26" in length. Also in this year, Remington began marketing Model 1100 SA Skeet guns in .410 and 28 gauge individually as standard models. These were available with 25" skeet choke barrels ($209.95).
1971
In this year Remington added a Model 1100 20 gauge Lightweight in 3" magnum gun, weighing 6lbs/12oz. Plain 28", full choke barrel guns cost $214.95, and vent rib guns cost $239.95.
1972
In January of this year, Remington Arms Company proudly advertised producing the one-millionth Model 1100 autoloading shotgun. In only nine years of production the Model 1100 exceeded that of the venerable Model 11 autoloading shotgun, which was in production for more than 45 years. That historic shotgun is serial numbered L509235M. Also in January, Remington introduced a reversed, mirror-image, Left-Hand version of the Model 1100 in 12 and 20 gauge guns in Field Grade 12 gauge (with 30" full choke, 28" modified, and 26" improved cylinder vent rib barrels), and 20 gauge (with 28" full and modified, and 26" improved cylinder vent rib barrels) , Magnum Grade 12 gauge only (with 3" chamber and 30" full choke, vent rib barrel) for $234.95, SA Skeet Grade 12 and 20 gauge (with 26" vent rib skeet barrel) for $224.95, and Trap Grade 12 gauge only (available with regular trap for $259.95, or Monte Carlo style stock, and 30" full choke, vent rib trap barrel for $269.95) variations.
1973
Remington introduced a special limited edition Model 1100 Ducks Unlimited Commemorative Shotgun, a 12 gauge chambered for 2 3/4" shells with full choke, vent rib 30" barrel. This shotgun was available only in 1973, and was dedicated to the Ducks Unlimited organization. The right side of the receiver was roll-stamped with a simple gold-colored scroll pattern. Centered on the left side of the receiver panel is a multi-colored bronze medallion depicting a canvasback duck, the Ducks Unlimited mallard head logo, flanked by decorative scroll work. At the lower left, stamped in gold-colored script is Remington Model-1100TM and on the lower right is the serial number preceded by DU. Six hundred of these guns were sold directly to DU Chapters for fund raising dinners in 1973, and 10,000 sold conventionally.
1974
Remington introduced the Model 1100 TBMC Trap Gun, in 12 gauge with 30-inch, vent rib barrel in full or modified trap chokes ($274.95). This gun featured a figured and checkered stock and fore-end, and had a rubber recoil pad. A Monte Carlo style stock was optional. A left-hand version of this gun was also available ($2 69.95). Due to a shortage of American walnut, in mid-year Remington began fitting some Model 1100 and Model 870 Field Grade shotguns with lightweight mahogany stocks and forends.
1976
In January, Remington introduced a 12 gauge Model 1100 TB Trap Gun in right and left-hand versions, with select American walnut in regular Trap or Monte Carlo style stock, rubber recoil pad, and ventilated rib. Advertising stated that this gun gives the shooter the All-Events competitive edge. Prices ranged from $314.95 to $329.95. To honor Americas Bicentennial Remington brought out four commemorative 12 gauge variations of the Model 1100: Model 1100 (28" plain barrel with modified choke); M1100 SA Skeet Bicentennial (26" vent rib with skeet choke for $284.95); M1100 TB Trap Bicentennial (30" vent rib with full choke for $319.95 with standard stock and $10.00 more for Monte Carlo stock); and M1100 TBMCS Trap Bicentennial (with 30" vent rib with full choke and Monte Carlo stock). Centered on the left side of the receiver panel is a gold-colored roll-engraved Bicentennial American Eagle and Shield with the dates 1776 and 1976 and scroll pattern. At the lower left stamped in script is Remington Model-1100 and on the lower right is the serial number. The right side of the receiver has simple scroll roll-markings in gold-color. Approximately 5,000 Bicentennial Model 1100 shotguns were sold.
1977
In March, Remington Arms Company proudly announced the manufacture of the two-millionth Model 1100 shotgun. Also in 1977, Remington introduced a new, redesigned Model 1100 20 gauge Lightweight (called LT-20) in Field Grade, Magnum and Skeet versions. These guns are visually distinguishable from previous 20 gauge models by the contoured ejection port (long barrel extension).
1978
The Model 1100 LT-20 (20 gauge) is available in a Field Grade version. Formerly, this gun was built on a larger 12 gauge frame. Concurrently, the Model 1100 20 gauge left-hand version was dropped, and was not available in LT-20 versions. The new Model 1100 LT-20 Deer gun replaced the older, large receiver 20 gauge Deer gun. The new gun had a 20", improved cylinder barrel with rifle sights. Stocks on all Model 1100 LT-20 Field guns now were being made of walnut instead of mahogany.
