Basque daily Gara published excerpts of the bulletin that the group released in April before it disbanded in May, marking the end of western Europe's last armed insurgency.
In it, ETA says it killed a total of 758 people since it emerged in 1959 — less than the 853 deaths attributed to the armed group by the Spanish government.
Among its victims were more than 320 Civil Guard and police agents and 101 military personnel, it adds, according to Gara.
It also admits to two attacks it had never claimed, such as an explosion in a Madrid cafeteria in 1974 that left 13 people dead.
All in all, ETA says it waged just over 2,600 armed actions.
Publication of the newsletter excerpts drew strong criticism from victims' group Covite.
In a statement, it said they showed ETA had disbanded “without repudiating its criminal trajectory nor condemning a totalitarian and discriminatory political project they tried to impose by force.”
In one assertion that drew criticism, ETA says the 1968 assassination of Meliton Manzanas, a high-ranking police officer under the Franco regime known as a torturer, was its first.
But historians say Civil Guard agent Jose Antonio Pardines was actually the first to be killed by the group earlier that year.
In its newsletter as quoted by Gara, ETA also lauds its actions against a planned nuclear power plant in the Basque town of Lemoiz which was deeply unpopular and was eventually dropped.
The Basque group targeted workers at the plant such as Jose Maria Ryan, a 39-year-old father of five who was production manager there.
ETA kidnapped him in January 1981, giving authorities a seven-day ultimatum to stop construction, and eventually executed him with a bullet to the head.
“Lemoiz showed the efficiency of the armed struggle in the eyes of wide sections of society,” Gara quotes ETA's bulletin as saying.
It is unclear though whether ETA's killings or Basque society's general opposition to the plant eventually led authorities to drop construction.
In the bulletin, ETA also condemns its 1987 attack on a supermarket in Barcelona that killed 21 people — its deadliest — as “the worst mistake and tragedy.”