you rejected this change because UW and Amboss disagree, but I found information from both UW and Amboss agreeing with the change seen above. Quoted from UW question 15118: “Stranger anxiety typically starts at age 6 months peaks at 8-9 months, and resolves by age 2 years.” Amboss says “Stranger anxiety: when an infant is fearful of unknown individuals. Expected ages: 6 months–3 years”
I didn’t look at the CDC’s website for additional information. As the card is written, I would say that stranger anxiety starts at 6 months.