As the first reviewer states the yoga sutras are extremely terse, giving the appearance of notes taken by a student attending a lecture. Consequently most of them can be and are, perfectly legitimately, interpreted differently by different people. Sometimes translations can be so variant that it is difficult to believe that they are translating the same text. Check two or three online translations to see what I mean.
Naturally, each translator will bring their own frame of reference to their translation given the amount of scope they have. However, I'm afraid Mr Iyengar has not just done this but actually added his own material to the translation. The first sutra is a good example. The Sanskrit is clear and means "Now follows instruction in yoga." Mr Iyengar translates this as " With prayers for divine blessings, now begins an exposition of the sacred art of yoga." Other sutras, too, are 50% Iyengar and 50% Patanjali, as well as many sutras with a lesser degree of interpolation.
This may be fine for Mr Iyengar's followers but those seeking to know exactly what Patanjali was saying should exercise caution. This book's saving grace is that it does provide a word by word breakdown of the Sanskrit, so you can spot the interpolations if you are inclined to go through the breakdown.