Thought this might help. This is from the singaporemath.com website.
Primary Mathematics Standards edition is an adaptation of Primary Mathematics to meet the Mathematics Contents Standards for California Public Schools, adopted by the California State Board of Education in 1997 for grades 1-5 as one of the approved textbooks. It is similar to the US edition but has some rearrangement of topics and some added units, primarily in probability and data analysis, negative number, and coordinate graphing. The standards edition components are not interchangeable with the US or third edition components.
They have a chart available
http://www.singaporemath.com/FAQ_Primary_Math_s/15.htm#WhichSeriesShouldWeUse to help explain the differences.
