APA-findings and a question

Hi, everybody. Sorry for late post.
I found something new for me and got one question about the APA style.
I want to share them with you here.

1. (pp. 49-51) Figure 2.1. Sample One-Experiment Paper (continued)

As we can see in these pages, we should write the title of the paper and the page number in the header.

2. (p.180) 6.22 Construction of an Accurate and Complete Reference List

In APA journals, Arabic numerals are used (e.g. Vol.3, not Vol.Ⅲ)

3. (p.183) 6.26 References included in a Meta-Analysis

In this page, the manual says:

If the number of articles contributing studies to the meta-analysis is relatively small

(e.g., about 50 or fewer), they should appear in the reference list with an asterisk

included to identify them.

But, I cannot understand this explanation.

So, my question is what is “the number of articles contributing studies to the meta-analysis”?