Roger my advice is to go to CompTIA's website and post your question on their blog since it's a CompTIA certification. Not sure you're going to get much information here but I could be wrong.
The Sec-501 is available, but the 401 is still available till May of next year. I would take the Sec+-401 since there is a lot changed and most material to be found is for the the 401.
I would recommend study and taking the 401. I would recommend Professor Messer - https://www.professormesser.com/security-plus/sy0-401/sy0-401-course-index/ . He also has material on the 501. It is free. He is really good and helped me pass mine back in the day. I would recommend attending the study groups once a month a few times to help. They are all recorded so you dont have to wait just grab and listen and test your self. Please let me know if you need any help.
Please let me know if you have any more questions on this be glad to help.
Remember Security+ is required for most government IT jobs.
Personally I would take the 401 exam and study as the content is so new for the 501 there is not much feed back on it yet. The book I used to pass was CompTIA Security+ Certification Bundle, Second Edition (Exam SY0-401) (Certification Press) by Glen E. Clarke. It was really good then went through the Professor Messer videos, the monthly study group videos were the best info, and I found the a lot of practice exams. This was the best for me.
Cybersecurity is a rapidly changing field. New threats are emerging every day. And while cybersecurity experts are developing countermeasures to these new risks, we are still behind the curve. Three years ago SY0-401 was released, on May 1, 2014, and since 2014, advances have grown significantly in the cybersecurity field. There is a severe need to develop, innovate, and evolve to enhanced technique and solutions for newly emerging cyber-security threats and vulnerabilities. Therefore, version SY0-501 has been designed and updated, to ensure the new risks and technique-methods are in consideration. Consequently, the replacement of SY0-401 is a necessity. Candidates who are preparing for the SY0-401 exam should not be discouraged because it is an active credential. However, if this is your vocation, it would behoove you to learn any new and improved changes that will enhance or influence your career.