Exactly, and there were times when redistricting simply wasn't done at the state level. It wasn't until 2 U.S.C. 2c was passed that the option of simply keeping the old plan despite a change in the number of seats was taken off the table.
Not so much an option, but a high level of forbearance. States that elected representatives at large for long periods of time were the exception. More typically, states redistricted immediately after a reapportionment, or at least within the decade.
25 states gained representation in 1912, and none lost any. By 1920 (first election for which Clerk of HoR has results), 23 were electing all representatives by district. The holdouts who elected the added representatives at large were Illinois and Pennsylvania. Pennsylvania switched in 1922 (no national reapportionment following 1920 census), and Illinois held out through the decade.
Following the 1930 census, 20 states lost representation. In 1932, 15 reduced the number of districts, and 5 states elected all representative at large (Kentucky (9), Minnesota (9), Missouri (13), North Dakota (2), and Virginia (9). Also, Vermont lost its 2nd representative, and elected its sole representative at large. 11 states, gained representation. 6 elected the extra representatives at large (Connecticut, Florida, New York, Ohio, Oklahoma, and Texas), while 5 redistricted. In addition, Illinois, which retained the same number of representatives, continued to elect two that it gained in 1912, at large.
By 1934, 4 of the 5 states that had lost representation in 1932 had redistricticted. North Dakota continued to elect its 2 representatives at large until 1962. Of the 7 gainers, 2 redistricted (Texas in 1934) and Florida in 1936), while the other 5 continued to elect some at large representatives.
In 1942, 9 states lost representation. 3 of them, Illinois, Ohio, and Oklahoma, had previously elected at large representatives. Illinois and Ohio, maintained the number of districts, while reducing the number of at large representatives from 2 to 1. Oklahoma dropped its single at large representative. 5 other states that lost representation, redistricted by 1942, and Pennsylvania apparently switched from 34 by district, to 32 district plus one at large (it had 32 districts before 1922, when it elected 4 at large).
Pennsylvania (1944) and Illinois (1946) switched to all district representatives, leaving Ohio (which elected a previous gained representative at large) as the only holdouts throughout the decade.
In 1942, 7 states gained representation, and 4 redistricted before the election, leaving Arizona, New Mexico, and Florida to elect one representative at large. Connecticut and New York continued to elect previously gained representatives at large.
Florida (1944), New York (1944), and Arizona (1948) switched to districts. New Mexico continued to elect its two representatives at large from 1942 to 1966, while Connecticut used a 5+1 plan from 1932 to 1962.
In 1952, 9 states lost representation and all redistricted before the first election. In addition, Ohio, which had previously elected at large representative after gaining two and losing one switched to all district elections. North Dakota, continued to elect 2 representatives at large throughout the decaded.
In 1952, 7 states gained representation, and 5 redistricted before the first election. The other 2 gainers, Texas and Washington redistricted in 1958, after electing an at large representative for 3 elections. Conecticut and New Mexico continued to elected previously gained representatives throughout the decade.
In 1962, 17 states lost representation. All but Alabama redistricted before the first election. Alabama became the last state to elect a large number of representatives (
at large, before redistricting in 1964. In addition, North Dakota a previous at large holdover divided into 2 districts for 1962.
In 1962, 9 states gained representation, 4 of which redistricted before the election. In addition there were two holdover gainers from the past.
Connecticut (1964), Michigan (1964), Maryland (1966), Ohio (1966), and Texas (1966) redistricted during the decade. 2 USC 2c was passed in 1967, and New Mexico redistricted for 1968. Hawaii was the last holdout for an at large election, not districting until 1970 (2 USC 2c provided an exception for the 91st Congress - elected in 1968 - that permitted states that had always elected its representatives at large to do so for that one final time.