I grew up in the southwest, and from anglos living there, often heard the intentional imperfection in the rug story. Navajo blankets often have imperfections, but there is always a reason.

1. Design (which is mental, not diagrammed and laid out) is larger than the available material. Result- the end is finished up differently than the beginning.
2. Some weavers did not see 'one end different from the other' as wrong.
3. The 'lazy line.' There is a diagonal line or lines in the weave, often pointed out as 'intentional'.
The Navajo weaver weaves a width that is comfortable for her, without moving from side to side each time she does a row. Master weaver Mary Pendleton, who uses Navajo and Hopi techniques and who worked with them, explains in her book: "If he rug is wider than a comfortable weaving width, she weaves the area in front of her, then moves over and catches the other areas up to where she stopped with the first area. Where these two areas meet, there is a faint diagonal line called the 'lazy line. To join the two aread correctly, proceed as follows:
a. Starting with the right area, weave to the left a comfortable distance and bring your weft to the front. Change shed and weave back to the right edge.
b. Weave to the left but stop one warp thread to the right of the one you just turned on. Change shed and weave back to the right.
c. Continue as above but turn on succeeding warp threads to the right as you weave, forming a diagonal line. .......... and so on-. Get the book (reasonable) if you are interested in Navajo weaving.
Mary Pendleton, 1974 (and reprints), "Navajo and Hopi Weaving Techniques."
4. Old blankets were woven with hand spun and hand dyed wool. Some weavers stick to the old methods. Some have learned new techniques and some have become 'name' artists. Imperfections in hand work are normal. Many modern 'tourist' rugs are made with bought materials.

In the 1860s the Navajo were forcibly removed from their lands and their flocks, fields and orchards destroyed when Carson rounded them up and forcibly removed to flat eastern NM- "the Long Walk." Prior to this, Navajo women made fine blankets, the "golden age," using natural dyes, some brought in from Mexico, their own wool, and yarns reclaimed from Spanish blankets. The art died with the exodus, and, after they were able to return to their
homelands, they lived in poverty.
The U. S. government allowed licensed traders to come into the area. Some of these traders, recognizing that fine work would bring financial reward not only to themselves but to the Navajo, encouraged them to rekindle their arts, even providing pattern books, and developing the 'pawn' system. Hubbell, Bloomfield, Moore and others became legends; regional styles which acquired names developed, and blankets were sold in fine stores, by mail order, and to the wave of tourists coming to the West.
In the 1890-1900 period, aniline dyestuffs became popular, but natural dyes also continue to be used to the present day.