I think Yao is just a 白讀音(the pronunciation common people use), 一 is 文讀音 (Intellectual/educated used). 白讀音 is hard to manage, because only words are very frequently used can only read in 白讀音. Mandarin trends to use 文讀音 instead 白讀音, so you don't need to learn this.
Some 白讀音 you have to know:
字 文 白
一 i1 iao1(sometimes written in 幺)
六 liu4 lu/lou
伯 buo2 ba/bie/bai
血 xue4 xie3/xue3
剝 bo1 bao2
薄 bo1 bao2
削 xue1 xiao1
爪 zhua3 zhao3
给 ji3 gei3*
壳 qiao4 ke2*
露 lu4 lou4
色 se4 shai3
鈅 yue4 yao4(only used in 鈅匙)
角 jue2 jiao3*
覺 jue2 jiao3(jiao3 is the same as jue2, jiao4 is another meaning.)
落 luo4 lao4
.......
When there is a *, you should pronounce this sound rather than 文讀.
Always sounds mentioned above is still common used. The meanings are exactly the same.
1982 : I read i jiou ba er, But yao jiou ba er is also ok.
2010 : I read er lieng i lieng, er lieng yao lieng is ok.
2001 : I read er lieng lieng i, er lieng lieng yao is seldom heard.
And shanghainese don't say er for 2, they prefer liang兩。兩千一零年 is also used.
So don't learn this. People in different place have different accent. In my dialect, 柏/百 六/陸/綠 have the same sound. I always use xue3/xie3 for 血。