205 Basic Set
General Information
The following information has been collected from original newspapers, catalogs, and magazines, some of which are freely available for reference below. The rest can be found in the site’s gallery. No aggregate catalogs (BrickLink, Brickset, etc.) were used.
Advertised Part Count(s): 205 pieces
First Year Confirmed Available:
1965 (USA)
I’ve written an extensive article about the 1965 wave in particular.
1967 (Canada)
1967 Eaton's Christmas Catalog
Most Likely Retirement Date: 1971 (USA)
The 205 set was a permanent member of the basic set line introduced in 1965 and was in continuous production until the cancellation of the LEGO license. It appears in an idea book used throughout 1970-1971.
1972 (Canada)
I place Canadian retirement at 1972 as I have no evidence of Canadian production beyond that date. The latest possible production run would've been 1972.
Last Year Seen Available: 1973 (USA)
Fairbanks Daily News Miner, July 25th, 1973
Aliases: No. 205 Basic Set, Beginner Set, Starter Set
Retail Price(s): $4.95 (USA) / $5.95 (Canada)
Discounted Example(s): $3.99 (1968), $3.29 (1970), $1.99 (1973)
Rarity Score (Index): 1/7
Known Box/Packing Variants
The 205 Basic Set, having been in continuous production from 1965 to 1971/72, has several variants, more than other sets. It doesn't rival the 001 Gears, but it's certainly up there.
I'm currently unsure if the 205 had any plain box versions for catalog sales. One likely existed for JCPenney, but it should not be confused with the plain box Sears 244 Explorer Set, which was the same size box but came with its own exclusive manual. The inner tray will also either say 244 or 205 to help identification.
There are at least six US colorful box variants. Shown below are ranges the boxes were produced from:
1965 - two patents, "Ages 3 to 9" missing from front of box, still on side (this is not the only 1965 set missing the age range, as the 001/002 were as well. Contemporary sources back up the 1965 date for this variant):
1966 - two patents, "Ages 3 to 9" added:

~1967-68 - two patents, "FOR ALL AGES" on front:
~1968-1969 - eight patents, drawer/sleeve style box:
~1969-1970 - eight patents, "FOR ALL AGES" no longer on front, tabbed box with single piece gray tray. Notice how the set now has the name "Beginner Set". 1970 examples will have "Some parts..produced in Denmark" stickered somewhere on the box:

~1970-1971 - tabbed box/gray plastic inner tray, eight patents, "Some parts...produced in Denmark" printed on the front, and "FOR ALL AGES" missing.

The 205 was also available in Canada starting in 1967 and has at least two variants:
A 1967-70 tall box version:

Then a 1971-72 flat box version with plastic tray:

Box/Overview
The 205 Basic Set, while unassuming in terms of the parts within and its basic set designation, is quite interesting for its number of variants. As a result of its wide distribution, the set is incredibly common and thus serves as one of the best examples for box differences.
The 205 Basic Set also carries a similar design as other basic sets from 1965:
Shown below are the sides of the box, which were changed in 1970+ examples
And the drawer, which was also later updated:
And the back of the box, featuring the continuation of the elephant build that was seen on 1961-63 instructions (a personal favorite model of mine):
Contents
As usual, the image shown below is a general guide, not to be taken as law: