Shopify limits the results to 50 so as to balance the server load. As per shopify docs.
Don’t ever paginate a collection by more than 50, that’s how many products maximum you should query per page
The default pagination count is 50 if you don’t specify the limit.
You’ve to customize the Blog template directly to add the limit like following.
{% paginate blog.articles by [your-limit-count] %}
{% endpaginate %}
About the SEO reason. If you want to set SEO for different countries or different content. You should research about some 3rd SEO app on Shopify app store, that will be easier.
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