Since the original date of publication (1951), the Real Academia de la Lengua Española (guardian of the Spanish Language) officially removed the accents on some one-syllable words. The old spellings appear in the book. For example, in Chapter 31 (common irregular verbs), these words have changed:
Old form: ví, vió, dí, dió, fuí, fué
New form: vi, vio, di, dio, fui, fue
(NOTE: this is not a complete list!)
Old spellings also appear in exercises using these words.
These changes don't change the pronunciation of the words! Accent marks are used to show how a word should be written in accordance with the way it is pronounced. The rules on pronouncing weak-weak, weak-strong, strong-weak and strong-strong vowel combinations apply: so, for example, vio (new form) sounds the same as vió (old form).
This is a great book for learning Spanish. Don't let the age of it throw you.
My plug for a top-notch dictionary: get the Pocket Oxford Spanish Dictionary Second Edition (2000).